Torque Converter Rebuilders Association
July 2010Issue 10, Volume 8
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Torque Converter Forensics - Honda 740 CodesMany converter shops have reported having
Honda converters returned to their shops because of 740 codes. In most cases, the remedy was to install a new O.E.M. converter. This con-firmed that the code problem was due to an inter-nal converter issue and not due to any valve body or other non- converter related problems. Finding the cause of the 740 codes became a priority and a Root Cause Analysis (RCA) began. The first step of the RCA was to collect as many report-edly “failed” units as possible. There were many returned units available, but at first, there was no proven method for determining which converters were actually good and which were bad. The tra-
ditional method used by most transmission shops is to test the holding power of the clutch (foot/lbs of torque) with 40 psi of air over ATF applied to the piston, to create the clamping force. When the “failed” units were tested with this method, they all tested good. A better test method appeared to be in order. An equal number of known good converters were collected and another series of tests were performed on the combined samples. This time, each unit was tested by applying vary-ing amounts air pressure/clamping force. The pressure used for the test varied from 10 psi to 40 psi and was stepped up in 5 psi increments. When the tests were completed, there was a clear division in the 20 to 25 psi range that separated the good converters from the converters that had set a 740 code. Converters that previously tested good at 40 psi were now failing in the lower pres-sure range. An additional piece of information was also dis-covered during these tests. Converters with the least amount of clamping force had the largest volume of oil escaping from the exhaust hose on the test fixture. This proved that the poor clamping force was the result of an internal leak. Leaking converters were cut open and inspected. There are three (3) possible areas for the leaks to occur. One is where the friction material of the TCC (torque converter clutch) piston mates to the cover. Since a positive seal is possible in this area, the focus of the inspection moved to the two ar-eas where there is no provision for a positive seal. The other two areas (turbine shaft to turbine hub and turbine hub to TCC piston), rely on the clear-ance between the mating parts to establish their
seal. The most likely area for the leak seemed to be between the turbine shaft and the turbine hub, but to be certain, individual flow tests were performed on both areas on all converters. The leak between the input shaft and turbine hub on all converters (both known good and known bad) would flow between .2 gpm (gallons per minute) and .5 gpm. The leak between the turbine hub and the piston, on the other hand, would flow .8 gpm to 4.5 gpm. This leak was obviously a lot more severe. This test also explains why Honda started using a scarf cut Teflon seal in this area on its later mod-el converters. Since the diameters of the turbine hubs on the earlier and later model converters were the same, it would be possible to use the later model seal if a groove could be cut into the hard-ened surface of the earlier turbine hubs. To cut the
g r o o v e a special tool was fabricat-ed from a carbide grooving tool. The end of the tool was cut off, ro-tated 90
degrees, and re-welded. (Figure 2) The hardened surface turned out to be only a few thousands of an inch deep and the hub machined easily. Figure 3 is the turbine hub after the groove is cut, and Figure 4 is the same hub with the late model seal installed. The ultimate test was to put this con-verter into a vehicle with a 740 code. To date, the converters with the added sealing ring have a
100% success rate. The folks at Consoli-dated Vehicle Converters of Kettering, Ohio used an O-ring from a General Mo-tors (GM) 245 mm converter for its seal. Their converter tested best of the lot on the lock-up clutch test fixture (holding over 150 ft/lb of torque at 20 psi). (Fig-ure 5) You may be wondering why 20-
25 psi was the sweet spot for testing the Honda converters, rather than the 40 psi that worked on other units. Honda does not use the typical two-path apply and release circuit that is used in the 4R100, 4L60-E, 5R55E, and many other applica-tions Instead, it uses a three-path oil circuit that incorporates a converter by pass valve like the circuits found in some front wheel drive Fords; eg. CD4E, AX4N, and AX4S. For this reason the circuit is especially sensitive to outside variables such as restricted coolers and cross leaks. A re-striction in the cooler circuit will cause the torque converter check valve to open, which reduces ap-ply pressure. If the cooler circuit becomes more restricted, it will react on the valve and may posi-tion some valves in a partially stroked position. Honda converter charge oil comes from the charge oil circuit of the main regulator valve. With this design, charge pressure is often only half of what line pressure would be. This is why the lock-up clutches of the Honda converters need to be tested at 20 to 25 P.S.I. instead of the 40 P.S.I. that
is used on other units. By adding the groove and seal, con-verter builders are able to not only rebuild the unit, they are providing their customers a converter that is an improvement over the original early design.
Footnote: Clearance counts! Even though the seal cured the test converters, some of the late model Od-yssey converters that already have the O.E. seal, still have lock-up problems. The problem with these converters has
turned out to be a clear-ance issue. In the past, c o n v e r t e r technicians who were re-moving the bearing from the front of the 4R100 turbine hubs
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
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to make the clutches apply like the E40D converters learned that .080” to .090” clearance was necessary between the hub and cover. That same clearance is needed for most of the converters that use the E4OD style stack up. The bottom line is that you need sufficient clearance to allow the piston and/or hub to come to a com-plete stop on lock-up apply before contact is made with the cover. When GM’s testing proved that the piston was stopped be-fore it contacted the cover on the early 245 and 298 mm converters, they reasoned that it was safe to remove the friction material stops near the I.D. of those TCC pistons. Some Honda converters have as little as .045” clearance be-tween the piston and the bearing that rests in the cover. Any machining of the clutch apply surface on the cover or clutch bonding surface on the pis-ton will make this clearance even less. Figure 6 shows the proper clearance between the piston and bearing race. The outer bearing race normal-ly protrudes out of the cover about .030”. If the
One of the common areas of failure in the BW 310 converter is the wear at the center of
the piston as it contacts the turbine hub. This wear is due to the damper assembly splines being offset from the piston center causing the piston to contact the turbine hub and wear prematurely. Many rebuilders are repairing, or replacing the piston, but if the damper assem-bly is not centered with the piston it will wear out prematurely also. I have found that even though the damper assembly is centered with a turbine hub before riveting it to the piston, it will not always stay centered with the piston after the riveting process is complete. The best way I have found to keep the damper assembly centered, is to center the damper assembly on the piston with a turbine hub, then temporari-ly bolt it together with two 1/4 inch bolts across from each other and tack weld it at the bolts (see photo). Then rivet the remaining holes in the assembly leaving the bolts in place to keep the tack weld from breaking. After the other riv-ets are installed remove the bolts & replace with rivets. (Some rivets may have to be tapped in
due to the holes being slightly off center) This procedure will help keep the damper assembly centered to the piston preventing piston bore wear. The piston is now ready to be balanced.
Rob Hans, Norfolk Transmission
Tech Tip: Borg Warner 310 Piston Repair
piston comes into contact with the outer bearing race before the pis-ton comes to a complete stop during lockup apply, it will ro-tate the race in the cover. On occasion the
rotation of the race will recess the race down to a point that the top will be flush with the cover. This will affect both the overall height and clutch release clearance of the converter. To get the pis-ton to bearing clearance to the proper tolerance, measure the clearance between the piston and bearing outer race, then machine the front of the piston at the I.D. It is usually only necessary to remove about .030” to .040”.
Ed Lee, ©Sonnax 2010
Torque Converter Forensics continued
Figure 6It is with deep sorrow that we an-nounce the passing of David Perry. Dave began working for Raybestos in 1980, riding his bicycle to work, and
he transitioned through the ranks until he resigned to pursue other ventures in April of 2009. He pioneered coated torque converter friction rings for the af-termarket, establishing Raybestos as the leading supplier in the converter reman industry. As Business Development Man-ager, Dave found business in other mar-kets such as the motorcycle, golf cart, and ATV industry. Dave was an avid outdoorsman and mo-torcycle enthusiast. He liked things tidy, enjoyed going to races, would always provide the facts, and was never one to “sugar coat” a conversation. Customers came to appreciate his straightforward approach and knew they could come to him with a question or concern, knowing it would receive prompt attention.
R.I.P. David Perry(May 11, 1957-June 29, 2010)
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